An electron beam apparatus which includes a sample stage on which a sample is placed, and an electron optical system. The electron optical system includes an electron gun that generates a primary electron beam, an immersion objective lens that converges the primary electron beam on the sample, an ExB deflector that separates a secondary particle, which is generated from irradiation of the primary beam to the sample, from an optical axis of the primary beam, a reflecting member to which the secondary particle collides, an assist electrode which is located under the reflecting member, a plurality of incidental particle detectors that selectively detect a velocity component and an azimuth component of a ternary particle which is generated by the secondary particle colliding to the reflecting member, and a center detector that is located above the reflecting member.